1. Field of the Invention
This invention relates to the establishment of restoration paths in a communications network in which each of the nodes is arranged to operate autonomously a distributed restoration process, and also to networks having nodes arranged to operate the method of the present invention.
2. Description of Related Art
It is known, for example from the article "The Self-Healing Network: A Fast Distributed Restoration Technique For Network Using Digital Cross-Connect Machines", W. D. Grover, IEEE Globecom 87, to respond to an alarm indicating failure at a detecting node to initiate a realtime restoration process employing a simple flooding method to propagate restoration signatures (messages), and establishing connection on receipt of a return signature.
It is also known, for example from the article "Using Distributed Topology Update and Pre-planned Configurations to Achieve Trunk Network Survivability", B. A. Coan, W. E. Leland, M. P. Vecchi, A. Wainrib, L. T. Wu, IEEE Transactions on Reliability, Vol. 40, No. 4, October 1991, to restore a network using pre-planned configurations to cover specific failures. The method disclosed in this article is known as NETSPAR. The advantage of using pre-planned restoration is that once the failure has been identified the appropriate reconfiguration can be attempted immediately. In NETSPAR each node communicates with a central Network Management Centre (NMC) which is arranged to compute pre-planned restoration configurations for selected notional failures in the network. The pre-planned restoration details are held in the NMC which responds to the reporting of an alarm by a node to refer to the stored set of pre-planned restoration configurations and to send restoration instructions to all the nodes comprising a restoration configuration. NETSPAR has the disadvantages that if the failure is not covered in the stored restoration set the NMC selects the "nearest fit" configuration from the stored set, and also that the downloading of details to the nodes can be a time-consuming and complicated matter.